Abstract
It is indispensable to balance the proton conductivity and dimensional stability, as well as maintain the high long-term durability of proton exchange membranes (PEMs). Herein, we proposed the sandwich structure composite membrane containing a middle layer of sulfonated polyetheretherketone (SPEEK) sandwiched by two layers of hybrid polyimide (PI) nanofiber. The hybrid nanofibers were fabricated via in situ loading different contents of NH2-UiO-66 (NU6) onto PI nanofiber as proton acceptors for amino-functionalization, resulting in NU6@PI nanofibers (NP) with different forms of assembly. By incorporating three-dimensional nanofibers into SPEEK, the dimensional stability of the composite membrane was dramatically boosted. The –SO3H groups on SPEEK interact with –NH2 groups on NP to form long-range acid-base pairs and acid-rich layer along the NP-SPEEK interface, which can provide abundant proton-conducting sites for proton transfer. Significantly, the continuous and uniform assembly of NU6 on PI nanofiber can form a compatible interface with SPEEK, ensuring the reliability of the proton pathways and robust mechanical properties. Insufficient or excessive loads of NU6 will lead to an imperfect NP-SPEEK interface, resulting in discontinuous proton channels or forming numerous defects that hinder continuous proton transport. The composite membrane of 4NP-SPEEK-4NP (40%NU6@PI-SPEEK-40%NU6@PI) with consecutive and reliable proton transfer channels displays enhanced stress, optimal proton conductivity, and excellent H2/O2 fuel cell performance. The durability test at 60 °C and 100% RH for 32 days reveals that the proton conductivity retention and tensile strength of the composite membrane are 89.8% and 47.8 MPa, which are 33.8% and 52.7% higher than those of SPEEK, respectively. The prepared membranes not only can be potential candidates for fuel cells but also provides a useful strategy for the longtime effective construction and regulation of proton transport channels in PEMs.
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